Usually, electrografting of aryldiazonium salts results in the formation of covalently attached films <10 nm thick. In this work, we report on an electrografting procedure by which thick conducting films, even in the micrometer size range, can be formed on glassy carbon, gold, or stainless steel in a controlled manner. It is a prerequisite that the aryldiazonium salt contains a redox active moiety such as nitrobenzene, anthraquinone, or benzophenone to maintain charge propagation in the growing layer. In addition, electrografting proceeds only efficiently by way of using potential sweeping rather than electrolysis at a fixed potential. Sweeping is essential to continuously desorbing any physisorbed species that otherwise would clog the channels in the film and make it insulating. Cyclic voltammetry, polarization modulation infrared reflection absorption spectroscopy, ellipsometry, and profilometry are used to characterize the surfaces and, through this, explain the growth mechanism. Elucidation of the role of the substrate, solvent, and supporting electrolyte is included in the investigation.

This work features the controllability of surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate, initiated by a multilayered 2-bromoisobutyryl moiety formed via diazonium chemistry. The thickness as a function of polymerization time has been studied by varying different parameters such as the bromine content of the initiator layer, polarity of reaction medium, ligand type (L), and the ratio of activator (Cu(I)) to deactivator (Cu(II)) in order to ascertain the controllability of the SI-ATRP process. The variation of thickness versus surface concentration of bromine shows a gradual transition from mushroom to brush-type conformation of the surface anchored chains in both polar and nonpolar reaction medium. Interestingly, it is revealed that very thick polymer brushes, on the order of 1 μm, can be obtained at high bromine content of the initiator layer in toluene. The initial polymerization rate and the overall final thickness are higher in the case of nonpolar solvent (toluene) compared to polar medium (acetonitrile or N,N-dimethylformamide). The ligand affects the initial rate of polymerization, which correlates with the redox potentials of the pertinent Cu(II)/Cu(I) complexes (L = Me(6)TREN, PMDETA, and BIPY). It is also observed that the ability of polymer brushes to reinitiate depends on the initial thickness and the solvent used for generating it.

Various nitrophenyl-containing organic layers have been electrografted to glassy carbon surfaces using diazonium chemistry to elucidate the extent by which the layer structure influences the solvent (i.e., acetonitrile) accessibility, electroactivity, and chemical reactivity of the films. For most of these films, cyclic voltammetric and impedance spectroscopy measurements show that the electron-transfer process at the electrode is facile and independent of film thickness and structure. This is consistent with the occurrence of self-mediated electron transfers throughout the film with nitrophenyl groups serving as redox stations. Importantly, this behavior is seen only after the first potential sweep, the effect of which is to increase the porosity of the layer by inducing an irreversible desorption of nonchemisorbed material along with a reorganization of the film structure. From a kinetic point of view, the radical anions of surface-attached nitrophenyl groups are reactive toward the residual water present in acetonitrile. Thin layers (thickness of 1 to 2 nm) containing redox-active groups only in the outer part of the layer are protonated two to three times as fast as groups located in a more hydrophobic but still solvent-accessible inner layer. Hence, kinetic measurements can detect small differences in the layer environment. Finally, a deconvolution of the cyclic voltammetric response of an electrode grafted from 4-nitrobenzenediazonium discloses that roughly 25% of the overall signal can be attributed to the presence of 4-azonitrophenyl moieties introduced during the electrografting process.

Thick conductive layers containing anthraquinone moieties are covalently immobilized on gold using redox grafting of the diazonium salt of anthraquinone (i.e., 9,10-dioxo-9,10-dihydroanthracene-1-diazonium tetrafluoroborate). This grafting procedure is based on using consecutive voltammetric sweeping and through this exploiting fast electron transfer reactions that are mediated by the anthraquinone redox moieties in the film. The fast film growth, which is followed by infrared reflection absorption spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, ellipsometry, and coverage calculation, results in a mushroom-like structure. In addition to varying the number of sweeps, layer thickness control can easily be exerted through appropriate choice of the switching potential and sweep rate. It is shown that the grafting of the diazonium salt is essentially a diffusion-controlled process but also that desorption of physisorbed material during the sweeping process is essentially for avoiding blocking of the film due to clogging of the electrolyte channels in the film. In general, sweep rates higher than 0.5 V s(-1) are required if thick, porous, and conducting films should be formed.

Self-immolative polymers (SIPs) are promising members of the emerging class of recyclable polymers with the ability to end-to-end depolymerize to their monomers. Unfortunately, SIPs are often synthesized by cumbersome procedures at low temperatures in protected atmosphere. In this study, a SIP with a novel poly­(disulfide) backbone is introduced, using dl-dithiothreitol (DTT) as the monomer. Remarkably, poly­(DTT) can be produced by solid-state polymerization in a robust and easily scalable process by mechanically mixing DTT with 2,2′-dithiodipyridine as the end-capping agent. The new polymer possesses good thermal and chemical stabilities, but once its depolymerization is triggered, this proceeds smoothly within minutes to afford cyclic DTT because of a favorable intramolecular back-biting thiol–disulfide exchange reaction in the polymer backbone. As a proof of concept, the cyclic DTT waste was recovered, reduced to DTT monomer, and repolymerized in a closed-loop approach.